Method of producing creep resistance of pb-sb alloys

ABSTRACT

Lead-antimony alloys of improved creep resistance are prepared by means of a process comprising finish deformation at elevated temperature with light, i.e., less than 10 percent reductions.

United States Patent [191 Tilman et al.

METHOD OF PRODUCING CREEP RESISTANCE OF PB-SB ALLOYS Inventors: Milton M. Tilman; Robert L.

Crosby; Leander A. Neumeier, all of Rolla, M0.

The United States of America as represented by the Secretary of the Interior, Washington, DC.

Filed: May 22, 1974 Appl. No.: 472,388

Assignee:

US. Cl 148/11.5 R Int. Cl. C22c 11/00 Field of Search 148/1 1.5 R; 75/166 B References Cited UNITED STATES PATENTS 1l/1902 Lloyd 75/168 B Primary ExaminerW. Stallard Attorney, Agent, or FirmWilliam S. Brown ABSTRACT Lead-antimony alloys of improved creep resistance are prepared by means of a process comprising finish deformation at elevated temperature with light, i.e., less than 10 percent reductions.

5 Claims, No Drawings METHOD OF PRODUCING CREEP RESISTANCE OF PB-SB ALLOYS Lead-antimony alloys containing about 1 to 9 percent antimony are in common usage for a variety of applications such as chemical processing equipment, sound barriers, radiation shielding, roofing and flashing. Conventional processing procedures commonly produce usable, although not high, tensile strength in these alloys. Such procedures generally do not produce desirably high creep resistance. It has now been found, according to the invention, that creep resistance of Pb-Sb alloys containing up to about percent Sb may be substantially improved by the use of a processing procedure comprising breakdown deformation, cold or hot, with greater than about percent reduction per pass for about 67 percent, or greater, reduction of original thickness, followed by finish deformation of less than 10 percent per pass, and preferably about 5 percent per pass or less, at a temperature of about 100 to 200C.

The alloys of the invention consist essentially of lead and up to about 5 percent of antimony. The process of the invention has been found to be particularly beneficial in treatment of alloys containing about 0.25 to 2.0 percent antimony. Deformation will generally be by means of rolling, but other means such as press forming may also be used. These procedures, and the equipment employed, are conventional in the art of metal working. Rolling speed and lubricants are also conventional, and are not critical. Reheating between passes need be only long enough to restore the elevated temperature, and the workpiece is normally air cooled after the last rolling pass.

The following examples will serve to more particularly illustrate the invention and the advantages achieved thereby.

EXAMPLES Samples were initially prepared by means of the following procedure:

Sixteen pound heats of lead-antimony alloys consisting of corroding grade lead and antimony of 99.99 percent purity were melted in an induction furnace using MgO crucibles. The lead was brought to the molten condition and a ZnCl flux cover added. The required amount of antimony was added through the flux cover at approximately 420C. After cooling to approximately 400C, NaCl was added to the flux cover to thicken the flux and facilitate removal. The flux was skimmed and the molten alloy was cast at approximately 400C into two preheated (about 300C) steel slab molds. Upon removal from the molds, the slabs measured 0.69 inch X 4 inches approximately 7 inches and weighed approximately 8 lbs. each. A inch slice was cut from the riser end of each slab and discarded. Samples for chemical analysis were then filed from both riser and butt ends of each slab and each sample analyzed separately for antimony content.

By rolling, slabs were cut in half, each half measuring 0.69 inch X 4 inches X 3 inches to 3.5 inches. The slabs were preheated at either 125 or 175C for 1 hour. Re duction per pass was 20 percent based on the thickness obtained after the preceding pass. Kerosene was used as a lubricant. The slabs were reheated for 10 to minutes between each pass. Five passes at 125 or 175C were sufficient to reduce the slabs to 0.225 inch to 0.227 inch X 4 inches X 9 inches to 9.5 inches. These slabs were cut in half to 0.225 inch to 0.227 inch X 4 inches X 4.5 inches to 4.75 inches long and used as starting stock for finish rolling.

The final 26 percent reduction (based on original thickness of 0.69 inch) was made at either room temperature, 125 or 175C at consecutive reductions of either 5 percent per pass or 20 percent per pass based on the thickness obtained after each preceding pass. When rolling at 125 or 175C, the plate was preheated for 1 hour at the selected temperature and reheated for 10 to 15 minutes between each pass. Final dimensions were approximately 4.125 inches X 18 inches X 0.0625 inch. Standard 8 inches sheet tensile and creep speciments were cut longitudinally from the finished sheet.

Table 1 gives creep data for Pb-Sb alloys that were finish rolled at 5 to 20 percent reduction per pass at 125C. The marked improvement in creep rates for the 5 percent reductions is apparent. Furthermore, the im- 700-psi stress, tests at :3F

Table 2 lists creep data, in percent per year, for Pb-Sb alloys containing up to 5 percent Sb, that were processed in various ways including the process of the invention, after breakdown rolling in the range-of to C.

Column II of the table gives data for alloys finish rolled cold, i.e., near room temperature, for 26 percent reduction based on starting thickness. This procedure is similar to commercial practice, which is done at various reductions per pass.

Columns Ill and VI give data for alloys finish rolled at 175C for 26 percent reduction based on starting thickness, for 5 and 20 percent reduction per pass, respectively.

Column IV gives data for alloys finish rolled at room temperature at 20 percent reduction per pass prior to annealing at 220C, and with a final pass at 175C and 5 percent reduction.

Column V gives data for alloys finish rolled at room temperature at 20 percent reduction per pass prior to solution treatment at 235C and aging 10 to 12 days at 90F.

As seen from the data of table 2, there is a vast difference in creep rates between alloys finish rolled cold and those finish rolled hot with light passes. The data of column 111, where repeated light passes were given at elevated temperature, shows very low creep rates, i.e., high creep resistance, and creep rates about the same for alloys containing 0.5 to 5.0 percent Sb. In contrast, rolling at 175C with 20 percent reduction per pass does not result in low creep rate, as shown in column V1.

The data in column 1V show that a single pass at 175C and 5 percent reduction does not provide maximum benefits, although the Pb-l.0 Sb alloy is approaching the rate for repeated passes (column Ill).

thickness and (2) finish deformation of the alloy at a temperature of about 100 to 200C and with reduction per pass less than percent.

2. The method of claim 1 in which the alloy contains about 0.5 to 2.0 percent antimony.

3. The method of claim 1 in which the deformation is accomplished by rolling.

At room temperature. Last 26 pct total reduction at 5 pct per pass. "Finish rolled at 175C. Last 26 pct total reduction at 5 pct per pass.

TABLE 2 I II III IV V VI Sb, Finish rolled Finish rolled Annealed Solution Finish rolled wt pct cold, at 175C, 220C. 7 treated at 175C,

Reduction per pass 5 pct reduction last pass at 235C,

5 pct 20 pct. per pass at 175C. aged 10 to 12 20 pct reduction 5 pct reduction days F per pass Rolled at 10 pct reduction per pass to avoid cracking.

TABLE 3 1.0 pct Sb 2.0 pct Sb 5.0 pct Sb Finish Finish Finish Property rolled Invention rolled Invention" rolled Invention cold cold cold Tensile strength, psi 2890 3310 3180 3940 3630 4930 Yield strength, psi 1470 2160 1920 2920 2320 4080 (0.2% offset) Elongation in 2 inches, pct 47 44 47 37 62 34 4. The method of claim 1 in which the finish deformation is accomplished at a temperature of about 125", to C.

5. The method of claim 1 in which the finish deformation is accomplished at a reductions per pass of about 5 percent. 

1. A METHOD FOR TREATMENT OF LEAD-ANTIMONY ALLOYS, CONTAINING UP TO ABOUT 5 PERCENT ANTIMONY, COMPRISING (1) BREAKDOWN DEFORMATION OF THE ALLOY WITH REDUCTIONS PER PASS GREATER THAN ABOUT 10 PERCENT FOR A TOTAL REDUCTION OF AT LEAST ABOUT 67 PERCENT OF THE ORIGINAL THICKNESS AND (2) FINISH DEFORMATION OF THE ALLOY AT A TEMPERATURE OF ABOUT 100* TO 200*C AND WITH REDUCTION PER PASS LESS THAN 10 PERCENT.
 2. The method of claim 1 in which the alloy contains about 0.5 to 2.0 percent antimony.
 3. The method of claim 1 in which the deformation is accomplished by rolling.
 4. The method of claim 1 in which the finish deformation is accomplished at a temperature of about 125* to 175*C.
 5. The method of claim 1 in which the finish deformation is accomplished at a reductions per pass of about 5 percent. 